I ordered an MR initially too but once I found out there are still LRs out there I immediately asked my OA to look for one for me and he came through for me this past weekend. Though $3k may seem steep for an extra 50 miles of range, but seeing how I'm keeping the car for a long time (probably 10+ years), it was still a no brainer to me for 2 main reasons:
1) I can envision MANY instances in the future where I would say, "Damn, I wish I had 50 extra miles so I don't have to stop and charge right now" (think road trips)
2) As the battery degrades over time, the extra 50 miles will be more and more valuable
I live in CA so cold weather isn't a factor either. Since you say you're probably going to keep the car for a long time too, I say don't hesitate to get the LR.
Oh, and as an added bonus, I don't have to anxiously wait anymore for more MRs to be delivered to CA buyers, I got a delivery date immediately after my order was changed to LR.